I checked the blueprints, (as I am sure those of you who have purchased the blueprint CD already have), and found that the two ends that fit into the frame are round and 2.5mm in size... the holes are also 2.5mm so that would indicate a press fit to me.
I thought I had remembered that there was a retaining drift pin on the inside of the frame, but not according to the blueprints.
While I don't have a Luger with me at work
, also according the prints, you should be able to see the ends of the lanyard loop staple on the inside of the frame as the holes ARE drilled through. They may be staked in place.
IF the ends of the loop are machined to 2.5mm and the holes drilled to that size as well, the fit would be very tight, and if the loop were refrigerated, and the frame warmed up, insertion would be not so difficult... once the two parts were the same temperature, it would take substantial effort to remove the staple.
I would submit that if you find a loose lanyard staple as Ed Tinker has, someone has already attempted removal and it didn't just loosen from use.
Just my $0.02 worth of engineering/gunsmithing expertise...
